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Tractive effort GT46AC's

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  • Member since
    May 2020
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Tractive effort GT46AC's
Posted by Hamotchi on Saturday, May 9, 2020 8:19 AM

During the tractive effort calculation to get the maximum speed at for a corospondant Resistance for EMD GT46AC's (4300 HP) i found myself struggling to validate my answers.

  1. for the rolling resistance i used Davis Formula (1992 Canadian National variation) 
  • R = 1.5 + 18N/W + 0.03 + CaV^2/10,000W  
  • then multiplied it by the total weight of the train
  • convert it to kN

I got very small numbers

for example at 120km/hr of a total train weight 2295 T 

R=25.7 kN  is it an acceptable value!!

2. for the second part the gradient resistance for the same weight at 3%

R=674.kN

Can someone advise or share some real resistance values to compare

  • Member since
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Posted by timz on Tuesday, May 12, 2020 11:54 AM

You mean, is 25.7 kN enough to roll a train of 2295 tons (2000-lb tons) at 120 km/hr on the level? No, it isn't. Apparently you misread the formula -- the Davis formula and its variations are confusingly written.

Which isn't to say the formula will give the right answer when you read it right. But can you tell us what your formula actually says?

By the original Davis formula, the resistance of a passenger train, in pounds, on the level at speed V (in miles/hour) is A + BV + CV^2 where

A = 1.3 times the train's tonnage, plus 29 times the number of axles

B = 0.03 times the train's tonnage

C = 0.041 times the number of cars

Based on that, a 2295-US-ton train at 120 km/hr will demand about 87 kN.

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Posted by Overmod on Tuesday, May 12, 2020 4:03 PM

timz
You mean, is 25.7 kN enough to roll a train of 2295 tons (2000-lb tons) at 120 km/hr on the level?

I took it to mean the nominal drawbar pull observable (via, say, dynamometry) for his constant-horsepower unit at 120km/h.  That's a very different thing from (and probably much less than, as expected) the 'balancing' resistance from the train that the Davis formula would produce.

I haven't bothered to check the numbers, so someone should do the curve generation from HP/speed to drawbar pull/speed, and then plot balancing that to Davis resistance corresponding to the profile and conditions of a particular division.

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Posted by caldreamer on Tuesday, May 12, 2020 4:41 PM

Per the Progress Rail Technical Spcifications for the GT46AC's. the  tractive effort is 4500 BHP.

  • Member since
    February 2005
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Posted by timz on Tuesday, May 12, 2020 6:41 PM

Overmod
I took it to mean the nominal drawbar pull observable (via, say, dynamometry) for his constant-horsepower unit at 120km/h. That's a very different thing from (and probably much less than, as expected) the 'balancing' resistance from the train that the Davis formula would produce.

Note to readers: if you can't make sense of this, don't bother trying to.

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